Opening Balance is not calculated for all columns in TAR form

Our tax team expects to see an opening balance (where there is a closing balance in prior year) on all columns in the TAR form (i.e. for all TAR accounts). This is how they are currently producing the equivalent report in Excel. I couldn't find a way to achieve this. Is there a particular reason this is not calculated by default? Is there a way to achieve this by customisation (e.g. member formula)?